Method for producing a turbine rotor

ABSTRACT

A method of producing a turbine rotor, in particular a steam turbine rotor, is provided. A forged and machined existing steam turbine rotor having partially larger dimensions as dimensions of an intended rotor is provided. The form of the existing rotor is compared with the form of the intended rotor and a position of the intended rotor within the existing rotor is chosen. Material is applied by build-up welding on portions of the existing rotor where not enough material is present for machining the intended rotor at the chosen position. The intended rotor is produced at the chosen position by machining the existing rotor.

FIELD OF INVENTION

The claimed invention refers to a method for producing a turbine rotor, in particular a steam turbine rotor.

BACKGROUND OF INVENTION

Steam turbine rotors are large components manufactured from forged steel ingots. The size and mechanical properties required of the forging for satisfactory operation require specialized processing that only a few vendors in the world can provide. In order to obtain a new forging from one of the suppliers often takes in excess of a year or more. Accordingly the production of a new turbine rotor is very costly not only in financial terms but also in terms of time.

Steam turbine rotors wear out during their operation. Accordingly, it is necessary to repair worn steam turbine rotors and to return them to service. Rotors can be repaired mechanically. Such mechanical repairs include machining away damaged areas, modifying integral rotors to include separate components, or stress relieving to remove excessive hardness or distortion. In addition, rotors can be repaired by means of build-up welding and subsequent machining Build-up welding introduces the ability to restore a rotor to its original configuration with little to no detriment to performance or reliability. However, rotor welding can be a slow and expensive process, which can make large repairs difficult financially.

If a repair of a steam turbine rotor is not profitable due to excessive damages, the damaged rotor may be replaced by a spare rotor. Due to the fact, that the waiting period for a forging necessary to produce a new rotor is very long, as already mentioned above, customers often store a spare rotor in order to ensure that they can resume power generation as quickly as possible in case of an unrepairable rotor. However, the stocking of a new replacement rotor is accompanied by large expense.

SUMMARY OF INVENTION

It is an object to provide an alternative method for producing a turbine rotor of the above-mentioned kind, which is favorable in terms of time and expense.

In order to solve this object, a method for producing a turbine rotor, in particular a steam turbine rotor is provided, said method comprising the steps of:

-   a) Providing at least one forged and machined existing steam turbine     rotor having partially larger dimensions as the dimensions of the     intended rotor to be produced; -   b) Comparing the form of said at least one existing rotor with the     form of the intended rotor and choosing a position of the intended     rotor within said at least one existing rotor; -   c) Applying material by means of build-up welding on portions of     said at least one existing rotor, where not enough material is     present for machining the intended rotor at the chosen position; and -   d) Producing the intended rotor at the chosen position by machining     the existing rotor.

Thus, according to the method of the claimed invention a new rotor is produced on the basis of at least one existing rotor, which may be provided in form of a salvaged or spare rotor having predominantly larger dimensions as the dimensions of the intended rotor to be produced. The intended rotor is fitted in the at least one existing rotor by means of a comparison of the form of the at least one existing rotor with the form of the intended rotor in order to choose a favorable position of the intended rotor within said at least one existing rotor, wherein the fitting may be supported by a corresponding computer program. At positions, where not enough material is present for producing the intended rotor at the chosen position by means of machining, additional material is applied by means of build-up welding on the respective portions of the at least one existing rotor. Subsequently, the intended rotor is produced at the chosen position by machining the existing rotor.

Preferably, the choice of the position of the intended rotor within said at least one existing rotor in step b) is made taking into consideration production-orientated aspects, in particular the amount of material to be applied in step c) and/or the amount of material to be machined in step d).

For example, the machining in step d) is performed by means of turning and/or milling and/or grinding.

According to one embodiment, at least two forged and machined existing steam turbine rotors are provided and joined to each other in step a), in particular by means of welding. Accordingly, the new rotor is produced on the basis of two existing rotors, which may be provided in the form of salvaged or spare rotors.

According to another embodiment, one or both of said at least two forged and machined existing steam turbine rotors are shortened prior to their joining in order to create a favorable basis for the production of the new rotor.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and aspects of the claimed invention become apparent by means of the following description of a method for producing a turbine rotor with reference to the accompanying drawing.

DETAILED DESCRIPTION OF INVENTION

The drawing schematically shows a steam turbine rotor 1, which is intended to be produced by the claimed method, and an existing steam turbine rotor 2 having predominantly larger dimensions as the dimensions of the intended rotor 1.

In a first step a) of the method, the existing steam turbine rotor 2 is provided. The existing rotor 2 may be a salvaged or a spare rotor being in stock. According to an alternative embodiment of the method, the existing rotor 2 may also be assembled of two or more existing steam turbine rotors, which are joined to each other in order to form the existing rotor 2, e.g. by means of welding, wherein the existing steam turbine rotors may be shortened prior to their joining

In a second step b) the form of the existing rotor 2 is compared with the form of the intended rotor 1 and a position of the intended rotor 1 is chosen within the existing rotor 2 taking into consideration production-oriented aspects, in particular the amount of material to be applied in step c) and/or the amount of material to be machined in step d). The comparison of the forms of the existing rotor 2 and the intended rotor 1 as well as the choice of the position of the intended rotor 1 within the existing rotor 2 may be supported by a suitable computer program, by means of which the intended rotor 1 can be fitted in the existing rotor 2 as indicated in the figure.

At portions A and B, where not enough material is present for machining the intended rotor 1 at the chosen position, it is necessary to augment the dimensions of the existing rotor 2 with a corresponding amount of weld material in an additional step c) by means of a build-up welding.

In a further step d) the intended rotor 1 is produced at the chosen position by machining the existing rotor 2, in particular by means of turning and/or milling and/or grinding.

One main advantage of the method is that it is superior to purchasing a new forging from both a cost and schedule perspective. It is also preferable to performing large-scale weld repairs where a significant percentage of the forging would have to be restored.

While specific embodiments have been described in detail, those with ordinary skill in the art will appreciate that various modifications and alternative to those details could be developed in light of the overall teachings of the disclosure. For example, elements described in association with different embodiments may be combined. Accordingly, the particular arrangements disclosed are meant to be illustrative only and should not be construed as limiting the scope of the claims or disclosure, which are to be given the full breadth of the appended claims, and any and all equivalents thereof It should be noted that the term “comprising” does not exclude other elements or steps and the use of articles “a” or “an” does not exclude a plurality. 

1. Method for producing a turbine rotor comprising: a) providing at least one forged and machined existing steam turbine rotor having partially larger dimensions as dimensions of an intended rotor to be produced; b) comparing the form of said at least one existing rotor with the form of the intended rotor and choosing a position of the intended rotor within said at least one existing rotor; c) applying material by build-up welding on portions of said at least one existing rotor, where not enough material is present for machining the intended rotor at the chosen position; and d) producing the intended rotor at the chosen position by machining the existing rotor.
 2. Method according to claim 1, wherein a choice of the position of the intended rotor within said at least one existing rotor in step b) is made taking into consideration production-orientated aspects, in particular the amount of material to be applied in step c) and/or the amount of material to be machined in step d).
 3. Method according to claim 1, wherein the machining in step d) is performed by means of turning and/or milling and/or grinding.
 4. Method according to claim 1, wherein at least two forged and machined existing steam turbine rotors are provided and joined to each other in step a).
 5. Method according to claim 4, wherein said at least two existing rotors are joined to each other by welding.
 6. Method according to claim 4, wherein one or both of said at least two forged and machined existing steam turbine rotors are shortened prior to their joining.
 7. Method according to claim 5, wherein one or both of said at least two forged and machined existing steam turbine rotors are shortened prior to their joining. 